System for constant flow generation of x-ray beams

ABSTRACT

A system for generating X-ray beams from a liquid target includes a vacuum chamber, a diamond window assembly, an electron source, a target material flow system, and an X-ray detector/imager. An electron beam from the electron source travels through the diamond window assembly and into a dynamic target material of the flow system. Preferably, the dynamic target material is lead bismuth eutectic in a liquid state. Upon colliding with the dynamic target material, X-rays are generated. The generated X-rays exit through an X-ray exit window to be captured by the X-ray detector/imager. Since the dynamic target material is constantly in fluid motion within a pipeline of the flow system, the electron beam always has a new target area which is at a controlled operational temperature and thus, prevents overheating issues. By providing a small focus area for the electron beams, the overall imaging resolution of the X-rays is also improved.

BACKGROUND Field of the Invention

The present disclosure relates to a method and system for X-ray beamgeneration from a liquid target. The method and system of the presentdisclosure provides improved X-ray imaging resolution and heatreduction.

Description of the Related Art

The use of X-rays has a significant impact on the healthcare industry.Identifying bone fractures, imaging soft tissues, and cancer radiationdiagnostics are some instances where X-rays are used in the healthcareindustry. Diagnostic X-rays are generally within a range of 20kiloelectron volt (keV)-150 keV whereas X-rays used for radiationtherapy are usually in the range of 4-20×1000 keV. Additionally, X-raysare also used in other industries such as the oil industry where X-raysare used to image rock samples. X-rays can also be used to imagematerial defects. In doing so, a higher resolution, which is greaterthan the resolution used in medical imaging, is required. In instanceswhere higher resolution is required, the physical constraints related toX-ray generation may lead to a reduction in overall production power.High resolution imaging at a higher power will lead to a reduction inimaging time as well. Thus, a system that generates high resolutionimages at a high production power value is required to address thedrawbacks associated with conventional X-ray generation methods. Ingeneral, if the resolution is high, the focal spot is considerably smalland the power must be lowered.

More specifically, power is defined as a ratio between energy and time(power=energy/time), and intensity is defined as a ratio between powerand area (intensity=power/area). A target material can only handle alimited intensity. Therefore, if the resolution is high and theresulting focal spot area is small, the intensity can be maintained ataccepted values by lowering the power.

In order to generate X-rays, electrons are initially accelerated in avacuum by an electric field towards a metal target. When the electronsdecelerate within the metal, X-rays are emitted. Electron decelerationcan occur in two routes.

In a first route, named Bremsstrahlung radiation, electromagneticradiation is produced by the deceleration of a charged particle whendeflected by another charged particle, typically an electron by anatomic nucleus. The moving particle loses kinetic energy, which isconverted into radiation (i.e., a photon), thus satisfying the law ofconservation of energy. The term is also used to refer to the process ofproducing the radiation. Bremsstrahlung has a continuous spectrum, whichbecomes more intense and whose peak intensity shifts toward higherfrequencies as the change of the energy of the decelerated particlesincreases. Since the distance between the nucleus and the electronscannot be controlled, the X-ray energy is random yet statisticallypredictable.

In a second route, named characteristic radiation, X-rays are producedwhen an element is bombarded with high-energy particles, which can bephotons, electrons or ions (such as protons). When the incident particlestrikes a bound electron (the target electron) in an atom, the targetelectron is ejected from the inner shell of the atom. After the electronhas been ejected, the atom is left with a vacant energy level, alsoknown as a core hole. Outer-shell electrons then fall into the innershell, emitting quantized photons with an energy level equivalent to theenergy difference between the higher and lower states. Each element hasa unique set of energy levels, and thus the transition from higher tolower energy levels produces X-rays with frequencies that arecharacteristic to each element.

Generally, when X-ray beams are to be generated, an electron beam isaccelerated and then plunged into a metal target such that both X-rayemitting methods can operate. If the desired energy range for the X-rayis within the range of 10 kiloelectron volt (keV)-150 keV, a majority ofthe energy from the electrons is converted to heat, and less than 1% isconverted into X-ray radiation. A target energy range of 20 keV-150 keVis preferred for better imaging contrast of human tissue based onthickness and atomic composition (electron density). The X-ray energyrequired to generate adequate contrast at reasonable penetration dependson the imaging subject. In particular, the thinner the imaging subject,the lesser X-ray energy is required. For example, when imaging a humanfemale breast during mammography, wherein the thickness of the breast isapproximately 4 centimeters (cm)-5 cm, the imaging process is performedwith an energy level within the range of 20 keV-40 keV.

The X-ray exposure, R, is approximately given by the formula

R=constant*T_(o) ²*Z*N_(c),

Where,

N_(c)—Number of incoming electrons;T_(o)—Energy of the incoming electrons;Z—Atomic number of the target bombarded by the incoming electrons;See Frank Attix, “Introduction to Radiological Physics and RadiationDosimetry”, Wiley-VCH 1991, incorporated herein by reference in itsentirety.

When generating X-ray beams in the medical field, the technologicalprocess involves generating an electron beam from a small hot filamentpositioned within a vacuum tube. The electron beam is accelerated to adesired kilovoltage (kV) level which is preferably within a range of 20kV-160 kV. The electron beam is then focused onto a small rectangularshape on a solid target, wherein the solid target is generally tungsten.The dimensions of the rectangular shape can be, but are not limited to,1.2 millimeters (mm), 0.6 mm, 0.3mm, and 0.1 mm. The dimensions can varyaccording to the line of focus principle, which determines the angle inwhich the target is positioned at relative to the incident electronbeam.

For imaging purposes, to generate an X-ray image, the X-ray beams needto be generated from a point source. The point source is obtained byfocusing the electron beams into a small focus region such that thesmall focus region turns into the X-ray source after the interactionwith the electron beams. The imaging resolution gets better as the focusregion gets smaller. However, cooling the focus region becomes achallenge due to the concentrated thermal energy. Therefore, in fixedtarget systems as shown in FIG. 1A, the focus region has to be keptlarge to prevent heat related damage. The thermal capacity of the targetthat contains the focus region, the conductivity properties of thetarget, and the boiling point of the target are some of the factors thatneed to be considered when using a fixed target for X-ray generation.

As illustrated in FIG. 1B, rotating the target is one approach used toaddress heat related issues. By rotating the target, the electron beamcontacts a region of the target that has been cooled down duringrotation. Even though rotating the target has allowed smaller focusregions, implementing and maintaining mechanical systems that allow thetarget to rotate can be challenging. Moreover, having to limit the heatthat is generated to be within the anode limits the overall length ofthe imaging session as well; see for example U.S. Pat. Nos. 7,852,987and 8,259,905, each incorporated herein by reference in theirentireties.

In view of the difficulties and drawbacks of existing X-ray generatingmethods, the present disclosure describes a system to generate X-raysthat may result in comparatively better imaging resolution. To do so,the present disclosure describes a system that may be used to increaseelectron beam intensity by replacing the conventionally fixed electronbeam target with a fluid target. The electron beam reaches the fluidtarget by passing through a diamond window with high thermalconductivity. The diamond window, which is solid and has high thermalconductivity, is in constant contact with the fluid target such that thefluid target maintains a temperature of the diamond window.

SUMMARY OF THE INVENTION

The system of the present disclosure includes a vacuum chamber, a thindiamond window assembly, an electron source, a target material flowsystem, and an X-ray detector/imager. The electron source and the thindiamond window assembly are positioned within the vacuum chamber. Thethin diamond window assembly is integrated into the target material flowsystem which carries a dynamic target material used for X-ray beamgeneration. A high atomic number material such as lead bismuth eutecticmay be selected as the dynamic target material. Since the dynamic targetmaterial is constantly flowing within a pipeline of the target materialflow system, overheating issues related to conventional X-ray generationsystems may be addressed. Moreover, since the electron beam is focusedon a smaller target area the overall imaging quality resulting from theX-ray beams may be improved.

Keeping in mind that electron beams can be directed using electric ormagnetic fields but x-ray beams cannot be directed in any easy way(e.g., there are no “x-ray optics” like lenses or reflectors), theelectron source is aligned with the thin diamond window assembly suchthat the electron beam is directed to the thin diamond window assembly.Since the thin diamond window assembly is integrated into the targetmaterial flow system, the electron beam travels through a diamond sheetof the thin diamond window assembly and collides with the dynamic targetmaterial. A direction of the X-ray beam produced upon collision istowards an exit window of the vacuum chamber. To do so, the thin diamondwindow assembly is angularly positioned relative to the electron source.The X-ray detector/imager, which is positioned outside the vacuumchamber and also aligned with the exit window, is used to detect theX-ray beams.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A is an illustration of X-ray beam generation from a fixed target.

FIG. 1B is an illustration of X-ray beam generation from a rotatingtarget.

FIG. 2A is a schematic diagram of the system of the present disclosure.

FIG. 2B is a schematic diagram of the system of the present disclosure,wherein a pipeline is covered by a heating coil of the temperaturecontrol unit.

FIG. 2C is an illustration of the anode being angularly positioned at alarge anode angle to the electron beam with a short filament length.

FIG. 2D is an illustration of the anode being angularly positioned at alarge anode angle to the electron beam with a long filament length.

FIG. 2E is an illustration of the anode being angularly positioned at asmall anode angle to the electron beam with a small filament length.

FIG. 3 is a detailed view of the thin diamond window assembly of thepresent disclosure.

FIG. 4 is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes afront metal stiffener, a rear metal stiffener, a front opening, and arear opening, wherein the rear metal stiffener traverses an externalsurface of the pipeline.

FIG. 5A is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes afront metal stiffener, a rear metal stiffener, a front opening, and arear opening that are pressed against an external surface of thepipeline with a clamping rim and a high temperature sealing, wherein therear metal stiffener is positioned along the external surface of thepipeline.

FIG. 5B is a detailed view of the thin diamond window assembly of thepresent disclosure illustrating the arrival of the electron beam and theprojection of the X-rays, wherein the thin diamond window assemblyincludes a front metal stiffener, a rear metal stiffener, a frontopening, and a rear opening that are pressed against an external surfaceof the pipeline with a clamping rim and a high temperature sealing,wherein the rear metal stiffener is positioned along the externalsurface of the pipeline.

FIG. 6 is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes afront metal stiffener, a rear metal stiffener, a front countersink hole,a rear countersink hole that are pressed against an external surface ofthe pipeline with a clamping rim and a high temperature sealing, whereinthe rear metal stiffener is positioned along the surface of thepipeline.

FIG. 7 is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes adiamond sheet, a front metal stiffener and a front opening, wherein thediamond sheet and the front metal stiffener are pressed against theexternal surface of the pipeline with a clamping rim.

FIG. 8A is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes afront metal stiffener, a rear metal stiffener, a front opening, and arear countersink hole that are pressed against an external surface ofthe pipeline with a clamping rim and a high temperature sealing, whereinthe rear metal stiffener is positioned along the external surface of thepipeline.

FIG. 8B is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes afront metal stiffener, a rear metal stiffener, a front countersink hole,and a rear countersink hole that are pressed against an external surfaceof the pipeline with a clamping rim and a high temperature sealing,wherein the rear metal stiffener is positioned along the externalsurface of the pipeline.

FIG. 9 is a detailed view of the thin diamond window assembly of thepresent disclosure, wherein the thin diamond window assembly includes adiamond sheet, a front metal stiffener, and a front countersink hole,wherein the diamond sheet is pressed against the external surface of thepipeline with a clamping rim.

FIG. 10 is a perspective view illustrating the thin diamond windowassembly attached to the external surface of the pipeline.

FIG. 11 is an illustration showing the dimensions used to model the thindiamond window assembly in computational fluid dynamics (CFD) analysis.

FIG. 12 is an illustration of the temperature distribution on liquidlead-bismuth eutectic with a fluid velocity 10 meters/sec (m/s).

FIG. 13 an illustration of the temperature distribution on liquidlead-bismuth eutectic with a fluid velocity 50 m/s. FIG. 14 is a graphillustrating the maximum temperature of the heating spot at differentX-ray powers.

FIG. 15 is a graph illustrating the unsteady maximum temperaturedistribution of the thin diamond window assembly at different X-raypowers.

FIG. 16 is a graph illustrating the maximum temperature of the thindiamond window assembly at different X-ray powers.

FIG. 17 is an illustration of the Von Mises stress distribution on adiamond sheet with a pressure value of 0.2 megapascal (MPa).

FIG. 18 is an illustration of the Von Mises stress distribution on thediamond sheet with a pressure value of 0.2 MPa when only a circular areawith a 5 millimeter (mm) diameter is exposed.

FIG. 19 is an illustration of the Von Mises stress distribution of thediamond window with a pressure value of 0.2 MPa when only a circulararea with a 3 mm diameter is exposed.

FIG. 20 is an illustration of the displacement of the diamond window inthe Z-direction with a pressure value of 0.2 MPa on a circular area witha 3 mm diameter.

FIG. 21 is an illustration of the Von Mises stress distribution of acopper sheet with a pressure of 0.2 MPa.

FIG. 22 is an illustration of the displacement of the copper sheet inthe Z-direction with a pressure value of 0.2 MPa on a circular area witha 3 mm diameter.

FIG. 23 is an illustration of the Von Mises stress distribution of acopper plate with a cut-through frustum and applied pressure of 0.2 MPa.

FIG. 24 is an illustration of the displacement of the copper sheet witha cut-through frustum in the Z-direction with a pressure value of 0.2MPa on a circular area with a 3 mm diameter.

DETAILED DESCRIPTION

All illustrations of the drawings are for the purpose of describingselected embodiments of the present disclosure and are not intended tolimit the scope of the present disclosure or accompanying claims.

The present disclosure describes a method and system that is used togenerate X-ray beams from a liquid target material. Since the electronbeam target is constantly flowing within a designated flow system, theoverheating issues related to conventional X-ray beam generating systemsare minimized and thus, the lifetime of the X-ray beam generating systemmay be extended. Furthermore, the regulated temperature of the liquidtarget material allows the electron beams to focus onto a smaller targetarea resulting in high resolution X-ray images. By using a high atomicnumber material such as a lead bismuth eutectic as the liquid targetmaterial, an increase in X-ray beam generation of approximately 12% maybe achieved compared to the X-ray beam generation from a tungstentarget. The use of the liquid target material may also aid in generatingX-ray beams with a higher intensity that leads to less imaging time.When used for biological imaging, less imaging time is beneficial withmotion artifacts that are generally known to degrade the resolution ofan X-ray image by causing signal changes. X-ray beams with higherintensity can also reduce the overall imaging time in material scienceimaging and industrial imaging processes where X-rays are used as anon-destructive testing method to verify the internal structure andintegrity of a specimen.

As seen in FIG. 2A, FIG. 2B, and FIG. 3, the system of the presentdisclosure comprises a vacuum chamber 100, a thin diamond windowassembly 200, an electron source 300, a target material flow system 400,and an X-ray detector/imager 500. The vacuum chamber 100 provides anon-oxidative environment for the cathode material to project electronsas an electron beam towards the anode. In addition, the vacuum preventsscattering of the electron beam by gas molecule which occurs if thevacuum is not in place. In order to do so, the electron source 300,which emits electrons as an electron beam, and the thin diamond windowassembly 200, which allows the electron beam to collide with a dynamictarget material 411, are positioned within the vacuum chamber 100. Inthis instance, the electron source 300 functions as the cathode whereasthe dynamic target material 411 functions as the anode. The electronsource 300 is positioned within the vacuum chamber 100 such that theelectron beam is aligned with the thin diamond window assembly 200.

As described earlier, the vacuum prevents scattering of the electronbeam. However, when the electron beam passes through the thin diamondwindow assembly 200, scattering may occur. A thinness of a diamond sheet201 of the thin diamond window assembly 200 minimizes the scattering.Moreover, diamond having a low atomic number also minimizes scattering.Furthermore, the electron beam can be focused to counteract scatteringwhile maintaining a direct line of sight between the cathode and theanode. In particular, the electron beam needs to strike the dynamictarget material 411 at an angle such that the generated X-rays proceedtowards an imaging subject through an X-ray exit window 101. Forexample, a normal incidence of the electron beam prevents the X-raysgenerated upon collision from exiting through the X-ray exit window dueto self-attenuation at the anode.

If the electron beam is normal to the dynamic target material 411, amajority of the generated X-rays will be absorbed by the dynamic targetmaterial 411 with the exception of mega voltage beams where most of theradiation is in the forward direction and the target anode isconsiderably thin. Therefore, as seen in FIG. 2A and FIG. 2B, the thindiamond window assembly 200 is angularly positioned at an anode angle600 such that a tangent line along the dynamic target material 411defines one edge of the generated X-ray field. FIGS. 2C-2E illustratethe field coverage variation of the X-ray beam according to the anodeangle 600. The imaging subject is always positioned at a 90-degree angleto the electron beam as the electron beam is incident to the thindiamond window assembly 200 since most of the x-ray radiation isgenerated around the 90-degree angle. As seen in FIGS. 2C-2E, a tradeoffexists between the field coverage on the imaging side and the anodeangle 600. The larger the angle the wider the field size is, and thebetter the power loading. However, the resolution diminishes due to thegeometric projection of the focal spot.

As illustrated in FIG. 2C, when a large anode angle and a short filamentlength are used, satisfactory X-ray field coverage is achieved. However,a small effective focal spot resulting from the large anode angle andthe small filament length limits the overall power loading. When a largeanode angle and a long filament length are used as illustrated in FIG.2D, satisfactory field coverage is achieved. However, a larger effectivefocal spot is required for higher power loading. When a small anodeangle and a long filament length are used as illustrated in FIG. 2E, theoverall field coverage is limited. However, the small effective focalspot resulting from the small anode angle and the long filament lengthallows high power loading. The anode angle 600 can be, but is notlimited to, a value between a range of 5 degrees(*)-25 °, preferably10°-20°, or about 15°.

For the electron beam to pass through the thin diamond window assembly200 and collide with the dynamic target material 411, which is in liquidstate, the thin diamond window assembly 200 is integrated into thetarget material flow system 400 that maintains the flow of the dynamictarget material 411.

A high atomic number material is used as the dynamic target material411, wherein the high atomic number material results in a strongerradiative interaction with the electron beam such that a high yield ofhigh energy X-rays are generated. In a preferred embodiment, a leadbismuth eutectic (LBE) is used as the dynamic target material 411.However, in other embodiments, alloys with relatively low meltingtemperatures of materials including, but not limited to, gallium,mercury, indium, tin, cadmium, lead, or bismuth, preferably excludingalkaline metals may be used as the dynamic target material 411.

When considering the properties of lead bismuth eutectic, lead (Pb) hasan atomic number of 82, whereas bismuth (Bi) has an atomic number of 83.When considering the composition, lead bismuth eutectic has 44.5% oflead and 55.5% of bismuth. The density of lead bismuth eutectic can beexpressed as 1106-1.293·T kilogram/cubic meter (kg/m³), wherein T is thetemperature in kelvins. The specific heat capacity, C_(p), is164.8−0.0394 T+0.0000125 T²−45600 T⁻² Joules per kilogram kelvin(J/kg-K), wherein the specific heat capacity may depend on the leadcomposition, when liquid lead bismuth eutectic has a lead compositionbetween 40% and 60%. The thermal conductivity, K, is 3.284−0.001617 T−2.305E-6 T² Watts per meter kelvin (W/m-K). The viscosity, μ, is0.000494 exp (754.1/T) kilogram per meter per second (kg/m-s).

The dynamic target material 411, which is in a liquid state, preferablyfulfills specific requirements to be used as a target material for theelectron beam. For example, thermal conductivity, specific heat, andkinematic viscosity allow exceptionally good heat transport from thefocal spot (the interaction zone of the electron-beam with the dynamictarget material 411) to the outside of a pipeline 405 facilitating theflow of the dynamic target material 411. As described earlier, in orderto get a high yield of high energy x-rays, it has to contain elementswith high atomic numbers. The vapor pressure must be low enough to allowhigh temperatures sufficient to contain the liquid metal within thepiping network. Additionally, other factors such as having a low meltingpoint, which is preferably below room temperature, need to be consideredwhen selecting the dynamic target material 411. Liquid lead bismutheutectic has a melting point within a range of 397.7K-398.1K. Near themelting point, the density of a liquid metal generally shows an almostlinear dependence on temperature. Pure lead has a melting point within arange 598K-601K, whereas pure bismuth has a melting point within a rangeof 543K-547K.

X-ray beams are generated from the radiative interactions of theelectrons with the dynamic target material 411. After an X-ray beam isgenerated, to direct the X-ray beam towards the X-ray detector/imager500, the thin diamond window assembly 200 and the target material flowsystem 400 are angularly positioned to the electron source 300. As aresult, the X-ray beam generated from the deceleration of electrons isdirected towards an X-ray exit window 101 of the vacuum chamber 100. Inparticular, the generated X-ray is directed along a path that isperpendicular to a projection path of the electron beam. The X-ray beamthat passes through the X-ray exit window 101 towards the X-raydetector/imager 500 that is positioned externally and adjacent to thevacuum chamber 100. Moreover, the X-ray beam passes through an imagingsubject when travelling towards the X-ray detector/imager 500. Fordetection purposes, the X-ray detector/imager 500 is linearly alignedwith the X-ray exit window 101.

One of the primary purposes of having a small focal spot is to improveimaging resolution. When the generated X-rays reach the X-raydetector/imager 500, the X-ray detector/imager 500 develops the image.The X-ray detector/imager 500 can include, but is not limited to, films,image intensifiers, computed radiography techniques, and solid statearray detectors. The solid state array detectors can be direct, whereX-rays generate the charge that is read by a detector element, orindirect, where X-rays generate light that is detected by a lightdetector either directly or after optical processing.

The electron beam travels from the cathode to the anode within a vacuum.In a preferred embodiment, the vacuum chamber 100 providing the vacuumenvironment is a tube that has gases removed and sealed duringmanufacturing process. However, the type of vacuum chamber 100 may varyfrom one embodiment to another. For the transmission of electrons,ultra-high vacuum (UHV) conditions need to be satisfied. Therefore, thevacuum chamber 100 will require pressure values lower than about 10⁻⁷pascal or 100 nanopascals (10⁻⁹ millibar, ˜10 ⁻⁹ ton), which can beachieved by pumping gas out of the vacuum chamber 100. Since one pumpmay not be able to operate from an atmospheric pressure value to a UHVpressure value, a series of different pumps is preferably used accordingto the appropriate pressure range of the pump. As a first step, aroughing pump, which is initially used to evacuate a vacuum system,clears a majority of the internal gas from the vacuum chamber 100. Next,one or more pumps that operate at low pressures are used to remove theremainder of the gas from the vacuum chamber 100. The low pressure pumpscan be, but is not limited to, turbomolecular pumps, ion pumps, titaniumsublimation pumps, non-evaporable getter (NEG) pumps, and cryopumps.

A turbomolecular pump works on the principle that gas molecules can begiven momentum in a desired direction by repeated collision with amoving solid surface. In a turbomolecular pump, a rapidly spinning fanrotor ‘hits’ gas molecules from the inlet of the pump towards theexhaust in order to create or maintain a vacuum.

Ion pumps are capable of reaching pressures as low as 10⁻¹¹ mbar. An ionpump first ionizes gas within the vessel it is attached to and employs astrong electrical potential, typically 3-7 kilo Volts (kV), whichaccelerates the ions to into the a solid electrode. Small bits of theelectrode are sputtered into the chamber. Gasses are trapped by acombination of chemical reactions with the surface of thehighly-reactive sputtered material, and being physically trappedunderneath that material.

NEG pumps, based on the principle of metallic surface sorption of gasmolecules, are mostly porous alloys or powder mixtures of Al, Zr, Ti, Vand Fe. These pumps help establish and maintain vacuums by soaking up orbonding to gas molecules that remain within a partial vacuum through theuse of materials that readily form stable compounds with active gases.Sintered onto the inner surface of high vacuum vessels, the NEG coatingcan be applied even to spaces that are narrow and hard to pump out,which makes NEG pumps very popular in particle accelerators wherespacing is an issue.

A cryopump is a vacuum pump that traps gases and vapors by condensingthem on a cold surface, but are only effective on some gases. Theeffectiveness depends on the freezing and boiling points of the gasrelative to the temperature of the cryopump. Cryopumps are sometimesused to block particular contaminants, for example in front of adiffusion pump to trap backstreaming oil, or in front of a McLeod gaugeto keep out water.

When considering the overall structure, the vacuum chamber 100 ispreferably a glass or metal envelope that can maintain a vacuumenvironment for the cathode and the anode. Because the production ofx-rays involves the interaction between filament electrons and the anodetarget, if any air were present, the electrons from the air wouldcontribute to the electron stream, causing arcing and damage to thetube. The glass envelope variety is generally made of borosilicate glassbecause it is very heat resistant. However, as these tubes age,vaporized tungsten from the filament deposits on the inside of the glass(called “sun tanning” because of the bronze discoloration of the glass),which causes problems with arcing and damage. The metal envelope varietyprovides a constant electric potential between the electron stream fromthe cathode and the enclosure, thereby avoiding the arcing problem andextending tube life. The X-ray exit window 101 is designed to minimallyinterfere with the X-ray beam generated when the electrons collide withthe dynamic target material 411. To do so, the X-ray exit window 101 ispreferably made to have a small thickness, wherein the thickness can be,but is not limited to being within a range of 0.020 mm-0.050 mm, 0.025mm-0.040 mm, and 0.025 mm-0.035 mm. The X-ray exit window 101 ispreferably made from low atomic number materials to minimize x-rayscattering and/or absorption. The X-ray exit window 101 is also designedto withstand the pressure differential between the interior of thevacuum chamber 100 and the atmospheric pressure outside the vacuumchamber 100. A wall thickness of the vacuum chamber 100 can be, but isnot limited to, being within a range between 2 mm-5 mm.

Preferably, the vacuum chamber 100 is positioned within a protectivehousing that provides solid, stable mechanical support. The protectivehousing is preferably a lead-line metal structure that also serves as anelectrical insulator and thermal cushion for the vacuum chamber 100.

In an X-ray generating system, the electrons pass through the vacuumchamber 100 from a cathode, which is the electron source 300, to theanode, wherein a high voltage is maintained between the cathode and theanode. Generally, the cathode includes a wire filament, typicallytungsten, which emits electrons when heated. The temperature of thefilament is controlled by a current flow to the filament. More electronsare produced with an increase in the current flowing to the filament.Cathodes that emit electrons by heating a filament are called hotcathodes and can be separated as directly heated cathodes and indirectlyheated cathodes. In directly heated cathodes, the filament itself is thecathode and emits the electrons directly. On the other hand, inindirectly heated cathodes, the filament is not the cathode but ratherheats a separated cathode consisting of a sheet metal cylindersurrounding the filament, and the cylinder emits electrons.

Indirectly heated cathodes are used in most low power vacuum tubes. Forexample, in most vacuum tubes the cathode is a nickel tube, coated withmetal oxides. It is heated by an internal tungsten filament inside, andthe heat from the filament causes the outside surface of the oxidecoating to emit electrons. The filament of an indirectly heated cathodeis usually called the heater.

As described earlier, the electrons emitted from the cathode aredirected towards a target anode that initiates the X-ray beam generationprocess. The system of the present disclosure describes using thedynamic target material 411, which is a liquid, as the target anode.Moreover, the system of the present disclosure utilizes the targetmaterial flow system 400 to accommodate the dynamic target material 411.As seen in FIG. 2A, to do so, in addition to the dynamic target material411 and the pipeline 405, the target material flow system 400 comprisesa pump 401, a reservoir 403, and a temperature control unit 409. Duringthe X-ray beam generation process, the dynamic target material 411 needsto be in fluid motion within the pipeline 405 such that a new targetarea is continuously provided to the electron beam generated at theelectron source 300. To do so, the dynamic target material 411, whichmay be in a solid state within the reservoir 403, is melted via aheating component of the temperature control unit 409 and maintained asa fluid by maintaining a temperature to be above a melting pointtemperature of the dynamic target material 411. Next, the dynamic targetmaterial 411, which is now in a liquid state, is pumped into thepipeline 405 with the pump 401. To do so, the reservoir 403 and the pump401 are in fluid communication through the pipeline 405. Morespecifically, the dynamic target material 411 needs to be maintained ata temperature above a melting point temperature. When the electron beamcontacts the dynamic target material 411, the temperature of the dynamictarget material 411 rises. The temperature of the dynamic targetmaterial 411 should be maintained such that the rise in temperature doesnot damage the thin diamond window assembly 200 and the boundariesbetween the target material flow system 400 and the vacuum chamber 100.

To ensure that the dynamic target material 411 is maintained above themelting point temperature at a preferred temperature, the reservoir 403,the pump 401, and the pipeline 405 are enclosed by the temperaturecontrol unit 409 which can vary from one embodiment to another. Thus,the reservoir 403, the pump 401, and the pipeline 405 are in directcontact with the temperature control unit 409. Further, the dynamictarget material 411 serves as a cooling medium for the diamond window200. The reservoir 403 contains a cooling sub-unit that prevents theliquid medium temperature to rise above the operating temperature range.The cooling sub-unit may be air cooled or water cooled. As seen in FIG.2B, in a preferred embodiment, the temperature control unit 409comprises a heating coil that is wrapped around the reservoir 403, thepump 401, and the pipeline 405. The temperature control unit 409 is alsoused to prevent the system from overheating, especially when atemperature rise occurs when the electron beam strikes the dynamictarget material 411. For the dynamic target material 411 to maintain theliquid state, the dynamic target material 411 is in thermalcommunication with the temperature control unit 409. Preferably, thepump 401 and the pipeline 405 can withstand high temperatures associatedwith the dynamic target material 411. Moreover, when lead bismutheutectic is used in a preferred embodiment, the temperature control unit409 will control the operating temperature of the dynamic targetmaterial 411 to be within 100 centigrade (° C.) the melting point of thedynamic target material 411. To further prevent heat related damage, theelectron beam is preferably pulsated with a duty factor. Therefore, thethin diamond window assembly 200 is allowed to dissipate heat in betweenpulses determined by the duty factor.

The overall volume of the dynamic target material 411 the reservoir 403can hold may vary from one embodiment to another. In a preferredembodiment, the reservoir 403 may hold a volume which can be, but is notlimited to, a volume within a range of 1 liter (L)-5 L, preferably 2 L-4L, or about 3 L. In general, the volume of the reservoir 403 needs to besufficient to circulate within the target material flow system 400 andthe temperature control unit 409.

As described earlier, the pump 401 is used to draw a volume of thedynamic target material 411 from the reservoir 403 and inject thedynamic target material 411 into the pipeline 405. In one instance, thepump 401 can inject the dynamic target material 411 into the pipeline405 with a velocity of 10 meters/sec (m/s). In another instance, thepump 401 can inject the dynamic target material 411 into the pipeline405 with a velocity of 50 m/s. As described earlier, the pump 401 needsto withstand high temperatures associated with the dynamic targetmaterial 411. Failure to do so can result in added maintenance costs,damaged final products, and increased personal hazards. Therefore, whenselecting the pump 401 to be used with the dynamic target material 411,the external pump construction and the internal pump construction needto be considered so that the pump 401 can withstand dimensional changesdue to thermal expansion. Preferably, the pump 401 used in the system ofthe present disclosure will comply with ISO 2858 and DIN 24256standards.

In a preferred embodiment, the temperature control unit 409 is a heatingcoil that is wrapped around the reservoir 403, the pump 401, and thepipeline 405. The heating coil converts electrical energy into heatthrough the process of Joule heating, where the passing of an electricalcurrent through a conductor produces heat. In particular, the resistanceencountered by the electric current while passing through the conductorproduces heat. When the heating coil is being used in a preferredembodiment, the material used in manufacturing the heating coil can beNichrome, Kanthal, Cupronickel, or Etched foil.

Nichrome, which has 80% nickel and 20% chrome, is preferred due to therelatively high resistance, and forming of an adherent layer of chromiumoxide when heated for the first time. The material beneath the adherentlayer will not oxidize and will prevent the wire from breaking orburning out.

Kanthal is the trademark for a family of iron-chromium-aluminium(FeCrAl) alloys used in a wide range of resistance and high-temperatureapplications. Kanthal FeCrAl alloys consist of mainly iron, chromium(20%-30%) and aluminum (4%-7.5%). The alloys are known for their abilityto withstand high temperatures and having intermediate electricresistance. As such, it is frequently used in heating elements.

Cupronickel or copper-nickel (CuNi) is an alloy of copper that containsnickel and strengthening elements, such as iron and manganese. Thecopper content typically varies from 60% to 90%.

Etched foil elements are generally made from the same alloys asresistance wire elements, but are produced with a subtractivephoto-etching process that starts with a continuous sheet of metal foiland ends with a complex resistance pattern. These elements are commonlyfound in precision heating applications like medical diagnostics andaerospace.

As described earlier, the pipeline 405 needs to be manufactured frommaterial that can withstand high temperatures associated with thedynamic target material 411. Furthermore, material compatibility withlead bismuth eutectic also needs to be considered when selecting amaterial for the pipeline 405. For example, high-nickel-containingmaterials, such as Stainless Steel-316L and Inconel-693, show anexcessive dissolution after staying for 500 or more hours in leadbismuth eutectic at 700° C. Liquid target materials generally have amelting temperature which is generally below 150° C. However, having thecapability to withstand temperatures up to 700° C. may be beneficialwith liquid target materials that have a higher melting temperature. Dueto the high solubility of nickel in liquid lead bismuth eutectic,materials such as stainless steel-316L and Inconel-693 cannot be used inthe pipeline 405. On the other hand, aluminum-based alloys may not beused due to their low melting temperature (˜660° C.), while titanium andrefractory metals may not be used due to their excessive oxidation inthe air. Therefore, ferritic steel containing no nickel may be acandidate for manufacturing the pipeline 405. For example, Kanthal maybe used due to the availability, absence of nickel, and high content ofchromium and aluminum, wherein chromium and aluminum are crucialelements for the formation of protective oxide layers.

In instances where the target material flow system 400 shuts down, andthe required temperature is not maintained within the target materialflow system 400, the dynamic target material 411 may solidify within thepipeline 405. In order to ensure that the dynamic target material 411 isin liquid state following a shutdown of the target material flow system40, the system of the present disclosure preferably performs a startupheating process for a predetermined time period. By doing so, the systemof the present disclosure ensures that the dynamic target material 411is in liquid state.

The electrons generated at the electron source 300 collide with thedynamic target material 411 flowing within the target material flowsystem 400 after passing through a diamond sheet 201 of the thin diamondwindow assembly 200. The thickness of the diamond sheet 201 is within arange of between 0.01 millimeters (mm) to 0.1 mm, with a preferablethickness that is within a range 0.02 mm to 0.08. The thickness of thediamond window can also be within a range from 0.03 mm to 0.06 mm, 0.04mm to 0.05 mm. As described earlier, the thin diamond window assembly200 is positioned within the vacuum chamber 100. Therefore, a frontsurface of the diamond sheet 201 is exposed to a vacuum environmentwithin the vacuum chamber 100. When integrating the thin diamond windowassembly 200 into the target material flow system 400, the diamond sheet201 is firmly fixed to a pipeline 405 of the target material flow system400 to prevent leakages of the dynamic target material 411. Whenintegrated, a rear surface of the diamond sheet 201 will undergo apressure of the dynamic target material 411 flowing through the pipeline405. In a preferred embodiment, the pressure is within a range of 0.1Megapascal (MPa)-0.5 MPa with a preferable pressure value ofapproximately 0.2 MPa. The pressure difference between the front surfaceand the rear surface may create a bending action on the diamond sheet201 since the diamond sheet 201 is terminally fixed to the pipeline 405.Thus, the diamond sheet 201 can be considered as a sheet subjected totransverse pressure. The brittleness of diamond along with the tensionand compression stresses created from the bending action may cause thediamond sheet 201 to fail. To address the issue, a front metal stiffener207 and/or a rear metal stiffener 209 are used in the thin diamondwindow assembly 200. The front metal stiffener 207 and/or the rear metalstiffener 209 are oriented to minimize interaction with the electronbeam. The front metal stiffener 207 and the rear metal stiffener 209,which are preferably copper sheets that are attached to the diamondsheet 201, and are used to minimize the overall stress distribution onthe diamond sheet 201. The front metal stiffener 207 and the rear metalstiffener 209 will preferably have a thickness within a range of 1 mm-2mm, with a preferable thickness of 1.5 mm when the diamond sheet 201 hasa thickness of approximately 0.03 mm. Even though diamond is used in apreferred embodiment, other materials that can be, but is not limitedto, beryllium, tungsten, and molybdenum metal foils may be used in otherembodiments of the present disclosure. The thin diamond window assembly200 must be made of material with high melting temperature.

To analyze the stress distribution, the diamond sheet 201 was modelledas a SHELL 181 element type, wherein the SHELL 181 element type issuitable for analyzing thin to moderately-thick shell structures. SHELL181 is a four-noded element with six degrees of freedom at each node:translations in the x, y, and z directions, and rotations about the x,y, and z axes. The degenerate triangular option should only be used asfiller elements in mesh generation. The modulus of elasticity, which isa measure of stiffness, was tested at 1,220,000 MPa (1.2 Gigapascal(GPa) with a Poisson's ratio of 0.2. The boundaries were restricted withzero displacement, wherein U_(x)=U_(y)=U_(z)=0, and a pressure of 0.2MPa was applied on the entire surface area to simulate the pressureapplied by the dynamic target material 411 flowing within the pipeline405. The resulting Von Mises Stress distribution, which is a value usedto determine if a material will yield or fracture, is shown in FIG. 17.According to the test results, the minimum stress value is 3.5 GPa andthe maximum stress value is 54 GPa. Therefore, with a tensile strengthvalue ranging from 0.8 GPa and 1.2 GPa, diamond will definitely fail.

To address the failing of the diamond sheet 201, a majority of thediamond sheet 201 was covered such that only a particular area isexposed to the electron beam from the electron source 300. For testingpurposes, when an area with a diameter of 0.5 millimeters (mm) wasexposed, as seen in FIG. 18, a maximum stress value of 0.829 GPa wasanalyzed which is a significant reduction from the 3.5 GPa stress value.

As shown in FIG. 19, when an area with a diameter of 0.3 mm was exposed,which still allows the electron beam to pass through and interact withthe dynamic target material 411, the maximum stress detected was 0.3GPa. The 0.3 GPa stress value is less than the failing tensile stressvalue for diamond, which is 1.2 GPa. The displacement of the diamondsheet 201 when a circular area with a diameter of 3 mm was exposed isshown in FIG. 20, wherein a through thickness displacement of thediamond sheet 201 is approximately 0.05633 mm.

The present disclosure describes using the front metal stiffener 207 andthe rear metal stiffener 209, to limit the exposure area of the diamondsheet 201. In a preferred embodiment, to analyze the effects of usingcopper in the front metal stiffener 207 and the rear metal stiffener209, a copper sheet is modelled as a SOLID 285 element type with amodulus of elasticity of 121,000 MPa and a Poisson's ratio of 0.34,wherein the modulus of elasticity and Poisson's ratio are temperaturedependent. When the copper sheet is modelled as a SOLID 285 elementtype, the modulus of elasticity and Poisson's ratio are obtained for theoperating temperature of the target material flow system 400. Sincelead-bismuth eutectic is used, the operating temperature of the targetmaterial flow system 400 is the melting temperature of lead-bismuth.Copper, which has a melting temperature around 1000° C., is selected dueto the melting temperature which is high compared to the dynamic targetmaterial 411 that has a low melting temperature and a high atomicnumber. In another embodiment, if the dynamic target material 411 has ahigh melting temperature, the stiffeners used in the thin diamond windowassembly 200 will be manufactured from a different material. As analternative to using a different material for the stiffeners, thecalculations of the stresses and displacements may be revised usingvalues of modulus of elasticity and Poisson's ratio at the desiredoperating temperature, which is the melting temperature of the dynamictarget material.

In a preferred embodiment, a copper sheet having a thickness of 1.5 mmand having a width and length matching the diamond sheet 201 is used.The Von Mises stress distribution on the copper sheet when 0.2 MPa isapplied is shown in FIG. 21. The displacement of the copper sheet in theZ-direction is shown in FIG. 22. The stress distribution and thedisplacement of the copper sheet is relatively small when compared tothe stress distribution and the displacement of the diamond sheet 201.

According to the tests, the maximum displacement of the copper sheets(0.01 mm) in the Z-direction is considerably smaller than the maximumdisplacement of the diamond sheet 201 (0.05 mm). Thus, if thedisplacement of the diamond sheet 201 is governed by the displacement ofthe copper sheet, the maximum displacement will not be greater than thedisplacement of copper. As a result, the diamond sheet 201 will notfail.

As seen in FIG. 4, in one embodiment, the thin diamond window assembly200 comprises a clamping rim 203, a high temperature sealing 205, adiamond sheet 201, a front metal stiffener 207, a rear metal stiffener209, a front opening 211 and a rear opening 213. The front metalstiffener 207 and the rear metal stiffener 209 are used to isolate atarget area on the diamond sheet 201 for the electron beam to collidewith and generate X-rays. To do so, the diamond sheet 201 is positionedin between the front metal stiffener 207 and the rear metal stiffener209. The front opening 211 and the rear opening 213 are used to guidethe electron beam towards the dynamic target material 411. In order todo so, the front opening 211 centrally traverses the front metalstiffener 207, and the rear opening 213 centrally traverses the rearmetal stiffener 209. Thus, by aligning the front opening 211 and therear opening 213 a beam channel is configured for the electron beam topass through the diamond sheet 201 and collide with the dynamic targetmaterial 411. When integrating the thin diamond window assembly 200 intothe target material flow system 400, the rear metal stiffener 209traverses into an external surface 407 of the pipeline 405. To securethe thin diamond window assembly 200, the front metal stiffener 207, thediamond sheet 201, and the rear metal stiffener 209 are attached to theexternal surface 407 of the pipeline 405 with the high temperaturesealing 205 and the clamping rim 203.

As seen in FIG. 5A and FIG. 5B, in another embodiment, the thin diamondwindow assembly 200 comprises a clamping rim 203, a high temperaturesealing 205, a diamond sheet 201, a rear metal stiffener 209, and a rearopening 213. The diamond sheet 201 is attached to the rear metalstiffener 209 opposite the pipeline 405 and is positioned in between thefront metal stiffener 207 and the rear metal stiffener 209. The frontopening 211 centrally traverses the front metal stiffener 207. The rearopening 213 centrally traverses into the rear metal stiffener 209allowing the electron beam to pass through the diamond sheet 201. Whenthe thin diamond window assembly 200 is integrated into the targetmaterial flow system 400, the rear metal stiffener 209 is positionedalong an external surface 407 of the pipeline 405, and front metalstiffener 207 and the diamond sheet 201 are secured against the externalsurface 407 of the pipeline 405, as seen in FIG. 10, with the hightemperature sealing 205 and the clamping rim 203.

As seen in FIG. 6, in another embodiment, the thin diamond windowassembly 200 comprises a clamping rim 203, a high temperature sealing205, a diamond sheet 201, a front metal stiffener 207, a rear metalstiffener 209, a front countersink hole 216, and a rear countersink hole215. As described earlier, the front metal stiffener 207 and the rearmetal stiffener 209 are used to isolate a target area on the diamondsheet 201 for the electron beam to collide with dynamic target material411 and generate X-rays. To do so, the diamond sheet 201 is positionedin between the front metal stiffener 207 and the rear metal stiffener209. The front countersink hole 216 and the rear countersink hole 215are used to allow the electron beam to travel towards the dynamic targetmaterial 411. In order to do so, the front countersink hole 216centrally traverses the front metal stiffener 207, and the rearcountersink hole 215 centrally traverses the rear metal stiffener 209.Thus, by aligning the front countersink hole 216 and the rearcountersink hole 215 a beam channel is configured for the electron beamto pass through the diamond sheet 201 and collide with the dynamictarget material 411. In particular, the purpose of using the frontcountersink hole 216 and the rear countersink hole 215 is to ensure thatthe electron beam has sufficient space to pass through to the dynamictarget material 411 without colliding with the front metal stiffener 207or the rear metal stiffener 209. When integrating the thin diamondwindow assembly 200 into the target material flow system 400, the rearmetal stiffener 209 is positioned along the external surface 407 of thepipeline 405. To secure the thin diamond window assembly 200 against thepipeline 405, the front metal stiffener 207, the diamond sheet 201, andthe rear metal stiffener 209 are pressed against the external surface407 with the high temperature sealing 205 and the clamping rim 203.

As seen in FIG. 7, in another embodiment, the thin diamond windowassembly 200 comprises a clamping rim 203, a high temperature sealing205, a diamond sheet 201, a front metal stiffener 207, and a frontopening 211. The diamond sheet 201 is attached to the front metalstiffener 207, and is positioned in between the pipeline 405 and thefront metal stiffener 207. The front opening 211 centrally traversesinto the front metal stiffener 207 allowing the electron beam to passthrough the diamond sheet 201. In addition to allowing the electron beamto pass through and collide with the dynamic target material 411, thefront metal stiffener 207 stiffens the diamond sheet 201 against thepressure gradient from the dynamic target material 411, which contains ahigh pressure compared to the vacuum chamber 100, which is at a lowerpressure. Thus, any deforming that may occur in the diamond sheet 201may be prevented. When the thin diamond window assembly 200 isintegrated into the target material flow system 400, the diamond sheet201 is pressed against the external surface 407 of the pipeline 405. Tosecure the diamond sheet 201 against the pipeline 405, the front metalstiffener 207 and the diamond sheet 201 are pressed against the externalsurface 407 with the high temperature sealing 205 and the clamping rim203.

As seen in FIG. 8A, in another embodiment, the thin diamond windowassembly 200 comprises a clamping rim 203, a high temperature sealing205, a diamond sheet 201, a front metal stiffener 207, a rear metalstiffener 209, a front opening 211 and a rear countersink hole 215.Since the dynamic target material 411 flow may be affected by the rearopening 213 which perpendicularly traverses into the rear metalstiffener 209, the use of the rear countersink hole 215 may bebeneficial by providing an effective geometry enabling fluid flow. Theeffectiveness on the stress distribution was measured for a rearcountersink hole 215 having a first lateral base with a diameter withina range of 2 mm-6 mm and a second lateral base with a diameter within arange of 8 mm-12 mm. Preferably, the first lateral base has a diameterof 3 mm and a second lateral base has a diameter of 10 mm. When apressure of 0.2 MPa is applied, the Von Mises stress distribution andthe displacement in the Z-direction is shown in FIG. 23 and FIG. 24respectively. The test results show that the copper sheet can withstandthe pressure even with the use of the rear countersink hole 215. Thestress analysis tests conducted for both the diamond sheet 201 and thecopper sheet were linear elastic. If the diamond sheet 201 is sandwichedin between two copper sheets, the deformation of the diamond sheet 201will be governed by the copper sheets.

Similar to previous instances, the front metal stiffener 207 and therear metal stiffener 209 are used to isolate a target area on thediamond sheet 201 for the electron beam to pass through and generateX-rays by colliding with the dynamic target material 411. To do so, thediamond sheet 201 is positioned in between the front metal stiffener 207and the rear metal stiffener 209. The front opening 211 and the rearcountersink hole 215 are used to guide the electron beam towards thedynamic target material 411. In order to do so, the front opening 211centrally traverses the front metal stiffener 207 and the rearcountersink hole 215 centrally traverses the rear metal stiffener 209.Thus, by aligning the front opening 211 and the rear countersink hole215 a beam channel is configured for the electron beam to pass throughthe diamond sheet 201 and collide with the dynamic target material 411.When integrating the thin diamond window assembly 200 into the targetmaterial flow system 400, the rear metal stiffener 209 is positionedalong the external surface 407 of the pipeline 405. To secure the thindiamond window assembly 200 against the pipeline 405, the front metalstiffener 207, the diamond sheet 201, and the rear metal stiffener 209are pressed against the external surface 407 with the high temperaturesealing 205 and the clamping rim 203.

Similar to the embodiment illustrated in FIG. 8A, as seen in FIG. 8B, inanother embodiment, the thin diamond window assembly 200 comprises aclamping rim 203, a high temperature sealing 205, a diamond sheet 201, afront metal stiffener 207, a rear metal stiffener 209, a frontcountersink hole 216, and a rear opening 213. The front metal stiffener207 and the rear metal stiffener 209 are used to isolate a target areaon the diamond sheet 201 for the electron beam to collide with andgenerate X-rays. To do so, the diamond sheet 201 is positioned inbetween the front metal stiffener 207 and the rear metal stiffener 209.The front countersink hole 216 and the rear opening 213 are used toguide the electron beam towards the dynamic target material 411. Inorder to do so, the front countersink hole 216 centrally traverses thefront metal stiffener 207 and rear opening 213 centrally traverses therear metal stiffener 209. Thus, by aligning the front countersink hole216 and the rear opening 213 a beam channel is configured for theelectron beam to pass through the diamond sheet 201 and collide with thedynamic target material 411. When integrating the thin diamond windowassembly 200 into the target material flow system 400, the rear metalstiffener 209 is positioned along the external surface 407 of thepipeline 405. To secure the thin diamond window assembly 200 against thepipeline 405, the front metal stiffener 207, the diamond sheet 201, andthe rear metal stiffener 209 are pressed against the external surface407 with the high temperature sealing 205 and the clamping rim 203.

As seen in FIG. 9, in another embodiment, the thin diamond windowassembly 200 comprises a clamping rim 203, a high temperature sealing205, a diamond sheet 201, a front metal stiffener 207, and a frontcountersink hole 216. The diamond sheet 201 is attached to the frontmetal stiffener 207. The front countersink hole 216 centrally traversesinto the front metal stiffener 207 allowing the electron beam to passthrough the diamond sheet 201. When the thin diamond window assembly 200is integrated into the target material flow system 400, the diamondsheet 201 is positioned along the external surface 407 of the pipeline405 and is positioned in between the front metal stiffener 207 and theexternal surface 407 of the pipeline 405. To secure the thin diamondwindow assembly 200 against the pipeline 405, the front metal stiffener207 and the diamond sheet 201 are pressed against the external surface407 with the high temperature sealing 205 and the clamping rim 203.

Diamond is used for the electron beam window due to properties such asthe ability to withstand high temperatures from both the impact ofelectrons and the dynamic target material 411. In a preferredembodiment, the diamond sheet 201 has a thickness of 0.03 millimeters(mm), a length within a range of 24 mm-26 mm, and a width within a rangeof 24 mm-26 mm, with a preferable length and width value of 25.4 mm. Inother properties, diamond will have a density value within a range of3400 Kilogram/cubic meter (kg/m³)-3530 kg/m³, a thermal conductivityvalue K within a range of 9000 Watt per meter kelvin (W/mk)-1500 W/mk,and a specific heat capacity, C_(p), within a range of 620 Joule perkilogram kelvin (J/kgk)-650 J/kgk.

The high temperature sealing 205 is used to prevent leakages and attachthe diamond sheet 201 to the pipeline 405. The high temperature sealing205 can be, but is not limited to, a metal seal. Metal Seals areprimarily used in static applications for temperatures as high as 1000°C./1832 Fahrenheit (° F.) and pressures as high as 6825 bar/99000 poundsper square inch (psi) for select applications. At low cryogenictemperatures and low pressures, such as vacuum seal applications, metalseals are far better than polymers since they do not become brittle andlose elasticity. Metal seals also have a low leakage rate down to1×10⁻¹² cubic centimeters/sec per mm circumference, which in comparisonto high load O-rings is almost 100× better.

Unlike elastomer seals, metal seals are very highly resilient tocorrosive chemicals and intense levels of radiation. Such resiliencecoupled with the right material selection/coating for an application, ametal seal can be a very durable seal performing dependably for anextended time.

In one embodiment, Polytetrafluoroethylene (PTFE) may be used in thehigh temperature sealing 205. PTFE can resist strong industrialchemicals, and maintain integrity at temperatures above 500-Fahrenheit(° F.). In a different embodiment, Polyether ether ketone (PEEK) mayalso be used in the high temperature sealing 205. PEEK can resistchemicals, wear, and abrasions. In a different embodiment,Fluorosilicone may be used in the high temperature sealing 205.Fluorosilicone combines high liquid resistance of fluorocarbon, andextreme temperature stability of silicone. With a temperature above 400°F., Fluorosilicone O-rings can be exposed to sunlight, and will notdegrade due to air, ozone, aromatic, or chlorinated hydrocarbons. In adifferent embodiment, Silicone may be used as the high temperaturesealing 205. Silicone, which is a rubber like polymer, has a hightemperature resistance up to approximately 482° F. Furthermore, Siliconeis resistant to UV rays, ozone, and oxygen and has great electricalinsulation properties, and high gas permeability. Silicone is mainlyused to manufacture aerospace seals, and automobile gaskets.

When considering the operating temperatures, Silicon, Fluorosilicone,and Fluorocarbon have an operating temperature within a range of 375°F.-500° F., with a preferable range of 400° F.-500° F. EthylenePropylene Diene Monomer (EPDM) has an operating temperature within arange of 450° F.-500 ° F. with a preferable value greater than 400° F.Silicon sponge and conductive silicon have an operating temperaturewithin a range of −100° F.- +500° F. Silicone Coated Fiberglass has anoperating temperature of approximately 500° F./260° C.

The clamping rim 203 used in the system of the present disclosurepreferably fulfills the ISO-KF standards for clamp connections, DIN28404and ISO 1609, which are the standards for vacuum pipes starting from thediameter nominal (DN), DN63, and larger diameters used in fine and highvacuum systems.

Preferably, the clamping rim 203 and the pipeline 405 are manufacturedfrom the same material. For example, if the pipeline 405 is manufacturedusing Kanthal, the clamping 203 rim may also be manufactured fromKanthal. Using the same material for the clamping rim 203 and thepipeline 405 ensures that the clamping rim 203 can be convenientlyattached to the pipeline 405 via adhesive or welding. An advantage ofhaving the clamping rim 203 and the pipeline 405 made of the samematerial is that both the clamping rim 203 and the pipeline 405 willhave the same rate of expansion when heated since both components sharethe same coefficient of thermal expansion. Therefore, significantdevelopment of stresses/strains that occur due to thermal expansionmismatch can be prevented by using the same material for the clampingrim 203 and the pipeline 405. However, if a secure connection can beestablished between the clamping rim 203 and the pipeline 405, theclamping rim 203 and the pipeline 405 may be manufactured from differentmaterial.

Computational fluid dynamic (CFD) simulation can be performed on thethin diamond window assembly 200 to verify the applicability of thesystem. As seen in FIG. 11, the dimensions of the diamond sheet 201, 0.6mm×2.3 mm, are selected to simulate the use of the system of the presentdisclosure in medical computed tomography (CT) systems. In thisinstance, the power value of 10 kiloWatt (kW) is relatively high for aCT system corresponding to a 100 kiloVolt (kV) and 100 milliampere (mA)setting. The CFD simulation also gives information that the diamondsheet 201 will be sustained at a level well below the melting point.

Furthermore, an inlet temperature of 400 K and an inlet velocity of 10m/s and 50 m/s was considered during the simulation. The temperaturedistribution on the dynamic target material 411 at 10 m/s is shown inFIG. 12. The temperature distribution on the dynamic target material 411at 50 m/s is shown in FIG. 13. The focal point where the electron beamcollides with the dynamic target material 411 has a temperature of about9000K, which may cause the liquid bismuth eutectic to locally evaporate.However, the flow of the dynamic target material 411 within the pipeline405 allows the liquid bismuth eutectic to condense.

In external boundary conditions, a majority of the target material flowsystem 400 was exposed atmospheric air and the dynamic target material411 had a free stream temperature of 300 Centigrade (° C.). The dynamictarget material 411 also had a heat transfer coefficient of 20 Watts permeter² kelvin (W/m²-k). The heat inputs from the temperature controlunit 409 can be, but is not limited to, 10 kW, 50 kW, 100 kW, and 120 kWwherein the heat transfer from the temperature control unit 409 to thedynamic target material 411 can be, but is not limited to, conduction,convection, and radiation. The maximum temperature of a focal spot onthe diamond sheet 201 at different heat input values is shown in FIG.14. From the calculations related to the CFD simulation, an increase inX-ray beam generation of approximately 12% is calculated. The maximumunsteady and steady temperatures of the diamond sheet 201 with time isshown in FIG. 15 and FIG. 16, and as seen in the figures the maximumunsteady and steady temperatures for the diamond sheet 201 isapproximately 1100K for 10 kW is below the melting point for diamondwhich is 3000K. However, the temperature of the diamond sheet 201 at 120kW is 2000K which is still below the melting temperature.

The X-ray generation enhancement obtained when the system of the presentdisclosure is used can be calculated as follows:

Atomic number of lead bismuth eutectic=(82*0.445+83*0.555)=82.555,wherein 82 is the atomic number of lead and 83 is the atomic number ofbismuth. Furthermore, 44.5% is the percentage of lead in lead bismutheutectic and 55.5% is the percentage of bismuth in lead bismutheutectic. Next, the X-ray generation enhancement is calculated bycomparing the atomic number of lead bismuth eutectic with the atomicnumber of tungsten, which is 74, as follows: 82.555/74=1.116 =1.12. Thevalue is approximately 12% higher in Z number, wherein the X-raygeneration from electrons interacting with the dynamic target material411 is linear with the atomic number of the dynamic target material 411.

Terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups thereof.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items and may be abbreviated as“/”.

As used herein in the specification and claims, including as used in theexamples and unless otherwise expressly specified, all numbers may beread as if prefaced by the word “substantially”, “about” or“approximately,” even if the term does not expressly appear. The phrase“about” or “approximately” may be used when describing magnitude and/orposition to indicate that the value and/or position described is withina reasonable expected range of values and/or positions. For example, anumeric value may have a value that is +/−0.1% of the stated value (orrange of values), +/−1% of the stated value (or range of values), +/−2%of the stated value (or range of values), +/−5% of the stated value (orrange of values), +/−10% of the stated value (or range of values),+/−15% of the stated value (or range of values), +/−20% of the statedvalue (or range of values), etc. Any numerical range recited herein isintended to include all sub-ranges subsumed therein.

Disclosure of values and ranges of values for specific parameters (suchas temperatures, molecular weights, weight percentages, etc.) are notexclusive of other values and ranges of values useful herein. It isenvisioned that two or more specific exemplified values for a givenparameter may define endpoints for a range of values that may be claimedfor the parameter. For example, if Parameter X is exemplified herein tohave value A and also exemplified to have value Z, it is envisioned thatparameter X may have a range of values from about A to about Z.Similarly, it is envisioned that disclosure of two or more ranges ofvalues for a parameter (whether such ranges are nested, overlapping ordistinct) subsume all possible combination of ranges for the value thatmight be claimed using endpoints of the disclosed ranges. For example,if parameter X is exemplified herein to have values in the range of 1-10it also describes subranges for Parameter X including 1-9, 1-8, 1-7,2-9, 2-8, 2-7, 3-9, 3-8, 3-7, 2-8, 3-7, 4-6, or 7-10, 8-10 or 9-10 asmere examples. A range encompasses its endpoints as well as valuesinside of an endpoint, for example, the range 0-5 includes 0, >0, 1, 2,3, 4, <5 and 5.

As used herein, the words “preferred” and “preferably” refer toembodiments of the technology that afford certain benefits, undercertain circumstances. However, other embodiments may also be preferred,under the same or other circumstances. Furthermore, the recitation ofone or more preferred embodiments does not imply that other embodimentsare not useful, and is not intended to exclude other embodiments fromthe scope of the technology.

As referred to herein, all compositional percentages are by weight ofthe total composition, unless otherwise specified. As used herein, theword “include,” and its variants, is intended to be non-limiting, suchthat recitation of items in a list is not to the exclusion of other likeitems that may also be useful in the materials, compositions, devices,and methods of this technology. Similarly, the terms “can” and “may” andtheir variants are intended to be non-limiting, such that recitationthat an embodiment can or may comprise certain elements or features doesnot exclude other embodiments of the present invention that do notcontain those elements or features.

Spatially relative terms, such as “under”, “below”, “lower”, “over”,“upper”, “in front of” or “behind” and the like, may be used herein forease of description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if adevice in the figures is inverted, elements described as “under” or“beneath” other elements or features would then be oriented “over” theother elements or features. Thus, the exemplary term “under” canencompass both an orientation of over and under. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.Similarly, the terms “upwardly”, “downwardly”, “vertical”, “horizontal”and the like are used herein for the purpose of explanation only unlessspecifically indicated otherwise.

The description and specific examples, while indicating embodiments ofthe technology, are intended for purposes of illustration only and arenot intended to limit the scope of the technology. Moreover, recitationof multiple embodiments having stated features is not intended toexclude other embodiments having additional features, or otherembodiments incorporating different combinations of the stated features.Specific examples are provided for illustrative purposes of how to makeand use the compositions and methods of this technology and, unlessexplicitly stated otherwise, are not intended to be a representationthat given embodiments of this technology have, or have not, been madeor tested.

All publications and patent applications mentioned in this specificationare herein incorporated by reference in their entirety to the sameextent as if each individual publication or patent application wasspecifically and individually indicated to be incorporated by reference,especially referenced is disclosure appearing in the same sentence,paragraph, page or section of the specification in which theincorporation by reference appears.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A constant flow system for generating X-ray beams from a liquidtarget, comprising: a vacuum chamber, wherein the vacuum chambercomprises an X-ray exit window; a thin diamond window assembly, whereinthe thin diamond window assembly is positioned within the vacuumchamber; an electron source, wherein the electron source emits anelectron beam towards the thin diamond window assembly, wherein theelectron source is positioned within the vacuum chamber and the electronbeam is aligned with the thin diamond window assembly; a target materialflow system, wherein a molten alloy comprising one or more selected fromthe group consisting of gallium, mercury, indium, tin, cadmium, lead,and bismuth, and wherein the molten alloy excludes alkaline metals whichis in thermal communication with a temperature control unit of thetarget material flow system passes into and out of the vacuum chamberalong a pipeline of the target material flow system, wherein the moltenalloy is a dynamic target material of the target material flow system;wherein the thin diamond window assembly is integrated into the targetmaterial flow system, wherein the beam of electrons contacts the dynamictarget material through a diamond sheet of the thin diamond windowassembly; the thin diamond window assembly being angularly positioned tothe electron beam, wherein the thin diamond window assembly allows theelectron beam to pass through and collide with the dynamic targetmaterial to generate an X-ray beam, wherein the angular positioning ofthe thin diamond window assembly allows the generated X-rays to beemitted towards the X-ray exit window; an X-ray detector/imager, whereinthe X-ray detector/imager is positioned externally and adjacent thevacuum chamber; wherein the X-ray detector/imager is positionedperpendicular to a projection path of the electron beam from theelectron source; and the X-ray detector/imager being aligned with theX-ray exit window, wherein the electron source, the diamond window, thetarget material flow system and the X-ray exit window are positionedwith respect to each other so that an X-ray beam generated at the thindiamond window assembly passes through the X-ray exit window toward theX-ray detector/imager passing through an imaging subject.
 2. The systemfor generating X-ray beams from a liquid target of claim 1, wherein thetarget material flow system comprises a pump, a reservoir, the pipeline,the temperature control unit, and the dynamic target material, whereinthe temperature control unit maintains a temperature of the dynamictarget material to be above a melting point temperature; the dynamictarget material being in fluid motion within the pipeline; the dynamictarget material being in thermal communication with the temperaturecontrol unit; the reservoir and the pump being in fluid communicationthrough the pipeline; and the reservoir, the pump, and the pipelinebeing in direct contact with the temperature control unit. 3-20.(canceled)